1. Field of the Invention
The present invention generally relates to an IP (Internet Protocol) telephone terminal and a method of searching for a destination for use in an IP network.
2. Description of the Background Art
Today, IP telephone terminals operative on the basis of VoIP (Voice over Internet Protocol) architecture are extensively used to accomplish telephonic conversation on the IP network. In VoIP systems, IP telephone terminals are allotted to IP addresses to be identified, thus requiring the IP address of a called IP telephone terminal in order to establish a call meant to the IP telephone terminal to be called. When calling, what is input to an IP telephone terminal is a telephone, i.e. subscriber, number of a called party or IP telephone terminal. In order to set up a call connection, a process is required for converting the telephone number of a called party to a corresponding IP address.
The standardized specifications H.323 of the ITU-T (International Telecommunication Union-Telecommunication Standardization Sector) regulates that a unit called gatekeeper perform the address conversion stated above. The gatekeeper holds a table listing the telephone numbers of IP telephone terminals which that gatekeeper controls and the IP addresses associated therewith.
How to set up a call from an IP telephone terminal to a called IP telephone terminal will generally follow the procedure as read below. At first, a connection is established from a calling terminal to a gatekeeper. After a connection has been established to the gatekeeper, the telephone number of a terminal to be called is entered into the calling terminal, being in turn transmitted to the gatekeeper. The gatekeeper finds out the IP address associated with the telephone number thus received and sends out the IP address to the calling terminal. The calling terminal receives the IP address from the gatekeeper and assembles an IP packet having its header including the IP address thus received. That IP packet, i.e. call connection request packet, is transmitted on the IP network to the called terminal.
The conventional system of setting up call connections in the way stated above requires the gatekeeper to store in its database the telephone numbers and the associated IP addresses of all the IP telephone terminals which that gatekeeper controls.
An increase of IP telephone terminals to be controlled by the gatekeeper gives rise to an extensive, huge amount of management data including the telephone numbers and IP addresses associated therewith in its database.
The gatekeeper, having such an extensive management database, would have to deal with too much communications traffic concentrated thereon, thus causing a difficulty that heavier traffic is incurred on the lines to the gatekeeper. In addition, the gatekeeper would have to conduct a search on the huge amount of data in its database for IP addresses associated with telephone numbers requested. That requires extensive time for searching and setting up calls over the network.
Moreover, it takes troublesome works to operate and maintain the database in which such a huge amount of data are stored so that dedicated operators or maintenance staff are required, thus expensive in maintaining or updating the database.
When such a single gatekeeper fails in searching on the database, entire call connections are also failed between IP telephone terminals.